In 1876, inside a third floor walk-up garret apartment in the Scollay Square section of Boston Mass., Alexander Graham Bell spoke the first sentence transmitted over telephone wires. Technical innovations have dramatically transformed the telecommunications industry over the past one hundred and twenty three years. For example, telecommunications switching systems have evolved considerably from “hand operated” systems in which one instrument was electrically connected (through a hierarchical switching network) to another through the intervention of a human operator who would physically plug one circuit into another. Such direct electrical connection of two or more channels between two points (at least one channel in each direction), a connection that provides a user with exclusive use of the channels to exchange information, is referred to as circuit switching, or line switching. Human operators have largely been replaced by systems which employ electronic switching systems (ESS, e.g., 5ESS), in which the instruments are automatically connected through the network by electronic systems. Nevertheless, such switching systems often still employ circuit switching, a technique which yields highly reliable service, particularly for such “real time” communications applications as voice, in which the momentary loss of a channel is annoying and repeated such losses are unacceptable. Electronic switching systems, such as the 5ESS may interconnect telephone instruments through circuit switching, employing time division multiplexing (TDM), for example. In order to ensure that end-users receive the appropriate quality of service, the switches typically monitor and periodically test the activity of the trunks and lines that carry the channels being switched. If a communications error occurs, the switch may employ a “loopback” to isolate, or determine the exact location of, the system component that caused the error. Once isolated through a loopback, the system may reconfigure itself so that data may be routed around the failed system component or take other corrective measures.
Additionally, a technique known as packet switching, may be employed is often employed for the transmission of data over telecommunications network. With packet switching data is transmitted in packets, and the communications channel is only occupied for the duration of a packet's transmission and, after the transmission, the channel is available for use by other packets being transferred for other users. The packetized transmission may be transmitted using asynchronous transfer mode (ATM) techniques. Asynchronous transfer mode (ATM) is a connection-oriented transmission technique that employs fixed-size blocks of data, called cells, each of which consists of a five octet long header and an information field that is forty-eight octets long. Like other switching systems, an ATM switch employs loopbacks to isolate failed components and, once isolated, to recover from a component failure.
Since both types of switching are currently employed in communications systems, some systems employ both ATM and TDM in a single, hybrid, switch, such as an “extended” ESS having both TDM and ATM connections. The ATM section of the device may employ a loopback to isolate errors in the system components to which it provides an interface, and the TDM section of the hybrid device may employ a loopback to isolate errors in the system components to which it provides an interface. However, there are no components that provide loopback capability across the ATM and TDM sections. Consequently, errors may occur in an area of hybrid device that is inaccessible to traditional loopback testing and the isolation and repair of system failures may thereby be significantly delayed.
A hybrid switching device, such as an “extended” 5ESS may include both a circuit switching side, in the form of it's switching core, and a packet switching side, in the form of a multi-service module (MSM, also known as Packet Driver). Such a switching device may be connected to other switching devices through cables containing numerous shared telephone circuits, the cables often being referred to as trunks or paths. In order to locate faults within a packet switching section of a hybrid switch, or along a length of a trunk or a path associated with the packet switching section of the switch, a loopback test may be performed to test various portions, of the path between circuit switched components and packet switched components. In this way, the failed section may be located and adjustments may be made to correct the failure.
However, there is no facility currently available for a circuit switched side to initiate a loopback test that includes any portion of the packet switched side of the switch, or, conversely, for a packet switched side of the switched to initiate a loopback test that extends to any portion of the circuit switched side of the switch. Because such facilities are not available, a circuit switched side may route a call to a failed area of the packet switched side. Consequently, the call could be dropped by the packet switching side. Similarly, a call originating on the packet switching side may be dropped by a failed component on the circuit switching side of the switch and, without a means for locating errors on the circuit switching side, the packet switching side may continue, obliviously, to send calls to a failed segment of the circuit side of the switch.
An apparatus and method that provides for loopback testing across circuit switched (e.g., TDM) and packet switched (e.g., ATM) boundaries would therefore be highly advantageous.